Electronic equipment including personal computers, audio and video equipment, electronic and medical diagnostic equipment among others generally include one or more printed circuit boards having various analog and digital electronic devices mounted thereon. The printed circuit boards are usually mounted and housed in an electrically grounded conductive cabinet, or chassis, which provides electromagnetic interference and electrostatic discharge shielding therefor, as is known.
In the personal computing industry, for example, a printed circuit board, referred to commonly as a motherboard, is mechanically and electrically coupled to a chassis and often to another printed circuit board, sometimes called a riser card, transversely mounted in the chassis relative thereto. In the past, motherboards, and printed circuit boards generally, were fastened with screw fasteners to threaded bosses protruding from the chassis interior. Some screws and bosses are metal thereby also providing an electrical coupling between the circuit board and the chassis. Screw fasteners however are susceptible to over-torquing, which may damage the circuit board. Misguided screw driving tools are another source of potential damage to the circuit board. Installation of screw fasteners, moreover, is often performed manually and is a suspected cause of physical maladies such as carpel tunnel syndrome.
U.S. Pat. No. 5,467,254 issued Nov. 14, 1995 and entitled "Supportive Guide for Circuit-Card Grounding Including Tracks Having Staggered Protrusions At The Proximal End of the Tracks" discloses printed circuit cards slidably disposed between rail members engagably mounted onto a computer chassis.
The personal computer industry has recently proposed the NLX Motherboard Specification, which includes a standard for mounting the motherboard in a computer chassis with a rail member. FIG. 5 of the present patent specification is a partial sectional view of a prior art rail member and ground clip assembly according to the NLX Motherboard Specification. The rail member 10 includes a ground clip 20 with a first end portion 22 disposed on a mounting surface 12 of a threaded screw boss 14 and in contact with a metal lead on a circuit board 30. A screw fastener, not shown, is disposed through an opening 32 in the circuit board 30 and into the threaded screw boss 14 so as to fasten the rail member 10 to the circuit board 30. A distal tip portion 24 of the ground clip 20 is retained in a slot 16 formed in the rail member 10, and an intermediate portion 26 of the ground clip 20 is biased into engagement with a chassis 34, thereby providing an electrical coupling between the circuit board 30 and the chassis 34.
To assemble the prior art NLX Specification ground clip 20, it must be disposed through a first opening and along a serpentine path in the rail member 10 and flexed prior to inserting the tip portion 24 thereof into the retention slot 16. This task is not readily performed in automated assembly operations, and when performed manually is arduous and likely a source of cumulative fatigue disorders. Also, fabrication of the first opening, the serpentine path, and the retention slot is costly, resulting from the relatively complex mold apparatus required. The prior art ground clip 20 also has a tendency to become misaligned relative to the rail member 10 prior to fastening the printed circuit board 30 thereon, complicating the process of fastening the rail member 10 to the circuit board 30. Additionally, the resiliency of the prior art NLX ground clip 20 has a tendency to degrade over time, particularly after repeated installations. Degradation of ground clip resiliency adversely affects the integrity of the electrical coupling with the chassis 34, resulting in increased contact impedance and resulting possibly in an open circuit condition. Also, the NLX rail member 10 is fastened with screw fasteners to the circuit board 30, which therefore remains subject to damage from over-torqued screws and misguided fastener tools.
The present invention is drawn generally toward advancements in the art of rail member and resilient electrical contact assemblies useable for mechanically and electrically coupling printed circuit boards to electrically conductive chassis.
It is an object of the invention to provide novel rail member and electrical contact assemblies that overcome problems in the prior art, that are economical, and that comply with the NLX Motherboard Specification.
It is another object of the invention to provide novel rail member and electrical contact assemblies that are relatively easy to assemble, both manually and especially in automated assembly operations.
It is also an object of the invention to provide novel rail member and electrical contact assemblies wherein the electrical contact is positively located and securely retained by the rail member, particularly the alignment of the electrical contact with a fastener bore of the rail member, prior to fastening the rail member to a printed circuit board.
It is a further object of the invention to provide novel rail members with improved electrical contacts, and more particularly resilient electrical contacts that are relatively firmly biased against the chassis, and resilient electrical contacts that are less likely to set, or lose resiliency, after prolonged use, thereby providing a relatively improved electrical coupling with the chassis.
It is another object of the invention to provide novel rail member and electrical contact assemblies that are relatively simply and quickly fastenable to printed circuit boards without tools, and without the risk of damage associated with over-torqued screw fasteners and misguided fastener driving tools.
It is a more particular object of the invention to provide novel rail member and resilient electrical contact assemblies comprising a stud protruding into an electrical contact opening of the rail member, wherein a first end portion of the electrical contact is disposed on a fastener boss proximate the electrical contact opening, a curved portion of the electrical contact protrudes at least partially through the electrical contact opening beyond a bottom side of the rail member, and the stud is disposed through an opening in the electrical contact so as to engagably couple the electrical contact to the rail member.
It is another more particular object of the invention to provide novel rail members having resilient electrical contacts with a first end portion disposed on a fastener boss, a curved portion of the electrical contact protruding at least partially through the electrical contact opening beyond the bottom side of the rail member, and a compression wave portion between the first end portion and the curved portion of the electrical contact for firmly biasing the curved portion thereof toward the chassis.
It is yet another more particular object of the invention to provide novel rail members fastenable to printed circuit boards with non-threaded rivet fasteners having a fastener body portion disposed and retained in a fastener bore of the rail member so that a partially split resilient head protrudes beyond the top side of the rail member and through an aperture in the circuit board. A fastener pin is retainably disposable into a bore of the fastener body portion and between the partially split resilient head thereof from the bottom side of the rail member so as to secure the circuit board to the fastener body portion.